Stocker for semiconductor substrates, storage method therefor and fabrication method for semiconductor device using the stocker

ABSTRACT

A stocker for semiconductor substrates comprises a container that is for containing the semiconductor substrates and composed of a casing having an open side and a removable lid for sealing the casing at the open side, an atmosphere control unit having a cavity through which a clean gas is passed to keep the inside pressure higher than the outside atmospheric pressure and a gas supply system for supplying the gas to the cavity, and a loadport for connecting the cavity with the container to prevent outside air from entering into the inside of the container. The loadport comprises a port door and a lid placement/removing unit. The lid placement/removing unit is configured to remove the lid from the container into communication between the cavity and the container, thereby allowing the inside of the container to have the same atmosphere as the cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2004-175006 filed on Jun. 14, 2004 including specification, drawings and claims is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a stocker for storing semiconductor substrates contained in containers under a clean environment, a storage method therefor and a fabrication method for a semiconductor device using the same.

(2) Description of Related Art

With the progression of fabrication processes for semiconductor devices, the process rule has varied. With variations in the process rule, the number of process steps has increased and the process margin has decreased. Furthermore, since various fabrication systems for semiconductor devices have different processing capacities, semiconductor substrates at which semiconductor devices are being formed need wait for being processed by a system for the next process step. As a result, the semiconductor substrates remain before the next process step. Usually, in order to prevent particles and chemicals from being deposited on the remaining semiconductor substrates, the remaining semiconductor substrates are stored in a stocker referred to as a clean stocker while being contained in clean containers.

Now that the processing precision for fabricating semiconductor devices has become finer, the atmosphere to which semiconductor substrates are exposed has been demanded to have higher-level cleanliness than ever before. Containers for wafers have been changed from open carrier boxes to pods with excellent airtightness and cleanliness, such as BOUPs (Bottom Opening Unified Pods) and FOUPs (Front Opening Unified Pods), according to the SEMI standard.

In this relation, higher cleanliness has been required for recent fine processing, and there has been a demand for a semiconductor fabrication method that can maintain a sufficient cleanliness and suppress the formation of a natural oxide film or the like. An example of such a method is one in which a container is provided with a supply inlet and a drain outlet to replace the atmosphere in the container with an inert gas, thereby allowing a certain amount of an inert gas to flow into the container while circulating the inert gas under a reduced pressure (see Japanese Unexamined Patent Publication No. 2003-92345).

FIG. 7 shows a cross-sectional structure of a known stocker for semiconductor substrates. As shown in FIG. 7, containers 300 each having a gas suction port 302 at the bottom of its casing and a gas inflow port 306 at its door surface are held on platforms placed in a stocker 400.

Gas suction means 442 are provided for the platforms and connected to the gas suction ports 302 of the containers 300. The stocker 400 is filled with a clean nitrogen (N₂) gas.

When in this state a gas in each container 300 are forcibly aspirated from the gate suction port 302 to provide a negative pressure in the container 300, a clean N₂ gas flows from the gas inflow port 306 into the container 300. As a result, the gas in the container 300 can be replaced with the N₂ gas.

Furthermore, a N₂ gas in the container 300 is always replaced by keeping the inside of the container 300 at a negative pressure, resulting in the maintained clean environment.

However, with increase in the number of components due to a complex structure of the known stocker, the failure rate and cost increase. The reason for this is that the container need always be kept at a negative pressure in the known stocker, the container must be provided with the gas suction port and the gas inflow port and each platform in the stocker must be provided with a gas remover. Furthermore, semiconductor substrates in the container are contaminated, because it is difficult to clean the container of a complex shape, for example, a chemical solution does not reach some parts of the container in cleaning the container, and the chemical solution or moisture remains even after the drying of the container. Furthermore, the arrangement and opening/closing operations of the pods over a few thousands of times deform the gas suction port and the gas remover. Therefore, pods cannot smoothly be placed on the platforms of the stocker. This problem was fatal to the reliability of the pods.

Moreover, an inert gas is forced to flow into the container by keeping the inside of the container at a reduced pressure. Therefore, the container is always under a reduced pressure. As a result, a large stress is applied to the container, leading to the shortened lifetime of the container. Furthermore, an irregular air current is produced in the container, leading to generation of particles.

SUMMARY OF THE INVENTION

The present invention is made to solve the above conventional problems, and its object is to provide a simple, low-cost and high-reliability stocker that can store semiconductor substrates under a clean environment without complicating the structures of containers, a storage method for semiconductor substrates and fabrication method for a semiconductor device using the stocker.

In order to achieve the object, the stocker of the present invention for storing semiconductor substrates contained in each container has a structure in which a gas in the container is replaced through an open side of the container through which the semiconductor substrates are removed/put from/into the container.

To be specific, a stocker for semiconductor substrates according to the present invention comprises: a container for containing the semiconductor substrates at which semiconductor devices are to be formed, said container being composed of a casing having an open side and a removable lid for sealing the casing at the open side; an atmosphere control unit having a cavity through which a clean gas is passed to keep the inside pressure higher than the outside atmospheric pressure and a gas supply system for supplying the gas to the cavity; and a loadport for connecting the cavity with the container to prevent outside air from entering into the container, wherein the loadport comprises a port door that can be brought into close face-to-face contact with one surface of the lid of the container and a lid placement/removing unit for placing the lid on the container and removing the lid from the container brought into close face-to-face contact with the port door, and the lid placement/removing unit is configured to remove the lid from the container into communication between the cavity and the container, thereby allowing the inside of the container to have the same atmosphere as the cavity.

According to the stocker for semiconductor substrates of the present invention, complex gas-replacing exhaust and inlet mechanisms need not be provided for the container and the loadport of the stocker. Since the structures of the container and the stocker are thus simplified, this can reduce the failure rate and cost and facilitates the cleaning of the container. Furthermore, since a gas in the container is replaced under a positive pressure, this can reduce the stress applied to the container. Therefore, the lifetime of the container can be lengthened. As a result, a low-cost and high-reliability stocker can be realized.

In the stocker for semiconductor substrates of the present invention, a pressure in the cavity is preferably 1.5 through 3 times higher than the outside atmospheric pressure. With this structure, a gas in the container can certainly be replaced.

In the stocker for semiconductor substrates of the present invention, it is preferable that the gas has a moisture concentration of 2% or less and contains three or less 0.12-μm-or-more-diameter foreign particles per one cubic foot. With this structure, the semiconductor substrates can be stored in the stocker under a clean environment. This can restrain a natural oxide film from being formed on the surface of each semiconductor substrate and particles from being deposited thereon.

In the stocker of the present invention for semiconductor substrates, the gas is preferably a nitrogen gas, an argon gas, a helium gas, or air. The use of these gases allows the semiconductor substrate to be stored with reliability.

In the stocker of the present invention for semiconductor substrates, the gas supply system preferably has a moisture remover for reducing the moisture concentration in the gas to 2% or less. With this structure, the moisture concentration in the cavity can certainly be reduced.

The gas supply system preferably has at least one of a particle-removing filter for removing particles from the gas by filtering the gas and a chemical filter for removing a chemical substance from the gas by filtering the gas. With this structure, a clean gas can certainly be supplied to the container.

The stocker of the present invention may further comprise a gas recovery line for recovering a gas exhausted from the cavity and returning the gas to the gas supply system. This structure can reduce the usage of the gas.

It is preferable that the stocker of the present invention further comprises: a sensor for measuring the concentration of at least one of moisture, an organic chemical component and an inorganic chemical component in the cavity; and a flow rate control unit for increasing the gas flow rate in the cavity when the measurement result of the sensor is above a predetermined value. This structure can certainly prevent the semiconductor substrate from being contaminated.

It is preferable that the stocker of the present invention further comprises: a defect inspection unit for inspecting the surfaces of the semiconductor substrates for defects; and a semiconductor substrate transport system for taking the semiconductor substrates from the container and transferring the semiconductor substrates to the defect inspection unit. With this structure, the state of the semiconductor substrates being stored can be checked and the semiconductor substrates can be inspected during their storage. This can shorten the turnaround time of a fabrication process for the semiconductor device.

It is preferable that, in the stocker of the present invention, the loadport further comprises an extendable delivery table for receiving/delivering the container from/to the outside. This facilitates the transfer of the container.

It is preferable that the stocker of the present invention further comprises: a lid storage section for storing a lid removed from the container by the lid placement/removing unit; and a lid transport unit for bidirectionally transferring the removed lid between the lid placement/removing unit and the lid storage section.

In this case, the loadport preferably comprises a plurality of loadports. This can reduce the space occupied by the stocker in the clean room.

It is preferable that the stocker of the present invention further comprises a recognition unit for, when the lid is removed from the casing, recognizing a combination of the lid and the casing such that the removed lid can again be fitted to the associated casing. Therefore, the lid can certainly be returned to the associated casing.

In the stocker of the present invention, the container is preferably a front opening unified pod.

A storage method for semiconductor substrates of the present invention comprises the steps of: containing semiconductor substrates at which semiconductor devices are to be formed inside a stocker having a cavity through which a clean gas is passed to keep the inside pressure higher than the outside atmospheric pressure, connecting the stocker with a container composed of a casing having an open side and a removable lid for sealing the casing at the open side; opening the lid while preventing outside air from entering into the container, thereby communicating the cavity with the container; and storing the semiconductor substrates while replacing a gas inside the container with a gas with which the cavity is filled.

According to the storage method for semiconductor substrates of the present invention, complex gas-replacing exhaust and inlet mechanisms need not be provided for the container and the loadport of the stocker. Since the structures of the container and the stocker are thus simplified, this can reduce the failure rate and cost and facilitates the cleaning of the container. Furthermore, since a gas in the container is replaced under a positive pressure, this can reduce the stress applied to the container. Therefore, the lifetime of the container can be lengthened. As a result, a low-cost and high-reliability stocker can be realized.

In the method of the present invention, a pressure in the cavity is preferably 1.5 through 3 times higher than the outside atmospheric pressure. Thus, a gas in the container can certainly be replaced.

In the method of the present invention, the cavity is preferably filled with a gas having a moisture concentration of 2% or less and containing three or less 0.12-μm-or-more-diameter foreign particles per one cubic foot. This can certainly prevent particles from being deposited on the semiconductor substrate.

In the method of the present invention, the gas is preferably a nitrogen gas, an argon gas, a helium gas, or air. This allows the semiconductor substrate to be stored with reliability.

In the method of the present invention, a gas exhausted from the cavity is preferably used while being circulated by returning the gas to the cavity. This can certainly reduce the usage of the gas.

It is preferable that the method of the present invention further comprises the step of connecting the cavity to the container through a loadport comprising a port door that can be brought into close face-to-face contact with one surface of the lid of the container and a lid placement/removing unit for placing the lid on the container and removing the lid from the container brought into close face-to-face contact with the port door, said loadport being placed in the cavity. This can certainly prevent outside air from entering into the container.

It is preferable that the method of the present invention further comprises the steps of: measuring the concentration of at least one of moisture, organic chemical components and inorganic chemical components in the cavity; and increasing the flow rate of a gas supplied to the cavity when the result obtained by measuring the concentration thereof is above a predetermined value. This can certainly keep the cavity and the inside of the container clean.

A fabrication method for a semiconductor device according to the present invention comprises a plurality of process steps for forming a semiconductor device at a semiconductor substrate and a storage step carried out between any two of the plurality of process steps, wherein in the storage step, a stocker to which a container is connected is used, said container containing the semiconductor substrate and being composed of a casing having an open side and a removable lid for sealing the casing at the open side, the stocker comprises: an atmosphere control unit having a cavity through which a gas having a moisture concentration of 2% or less and containing three or less 0.12-μm-or-more-diameter ambient foreign particles per one cubic foot is passed to keep the inside pressure at a positive pressure that is 1.5 through 3 times higher than the outside atmospheric pressure, and a gas supply system for supplying the gas to the cavity; and a loadport for connecting the cavity with the container to prevent outside air from entering into the container, wherein the loadport comprises a port door that can be brought into close face-to-face contact with one surface of the lid of the container and a lid placement/removing unit for placing the lid on the container and removing the lid from the container brought into close face-to-face contact with the port door, and the lid is removed from the container by the lid placement/removing unit so that the cavity is communicated with the container to allow the inside of the container to have the same atmosphere as the cavity.

According to the fabrication method for a semiconductor device of the present invention, the semiconductor substrate can be prevented from being contaminated during the processing steps. This can improve the yield in the fabrication process for the semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a stocker for semiconductor substrates according to an embodiment of the present invention.

FIG. 2 is a graph showing, when semiconductor wafers are contained in the stocker for semiconductor substrates according to the embodiment, the relationship between the pressure in the cavity and the percentage at which foreign particles are deposited on one of the semiconductor wafers (hereinafter, referred to as “foreign particle deposition percentage”).

FIG. 3 is a graph showing the relationship between the number of foreign particles in the cavity and the foreign particle deposition percentage when the semiconductor wafers are stored in the stocker for semiconductor substrates according to the embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the moisture content in the cavity and the foreign particle deposition percentage when the semiconductor wafers are stored in the stocker for semiconductor substrates according to the embodiment of the present invention.

FIG. 5 is a schematic view showing another example of a stocker for semiconductor substrates according to the embodiment of the present invention.

FIG. 6 is a perspective view showing how stockers for semiconductor substrates according to the embodiment of the present invention are combined together.

FIG. 7 is a schematic view showing a stocker for semiconductor substrates according to the known example.

DETAILED DESCRIPTION OF THE INVENTION

A stocker for semiconductor substrates according to an embodiment of the present invention will be described hereinafter with reference to the drawings.

FIG. 1 shows a cross-sectional structure of a stocker for semiconductor substrates according to the present invention. As shown in FIG. 1, the stocker 104 comprises an atmosphere control unit 122 and loadports 120 serving as ports through which containers 101 are connected to the atmosphere control unit 122.

Each container 101 is composed of a casing 103 having an open side and a lid 102 that can seal the container 101 by coming into close contact with or engaging with the casing 103 at the open side. Furthermore, comb-like wafer teeth (not shown) are provided inside the container 101, and a plurality of semiconductor substrates 100 can horizontally be supported by the wafer teeth with a certain distance vertically apart from one another.

The loadports 120 comprise one or more associated supporting tables 105, one or more associated port doors 106 and a lid placement/removing unit 121. The outside surface of the lid 102 of the container 101 supported on the supporting table 105 is brought into close face-to-face contact with the port door 106, and then the lid 102 is removed from the container 101 by the lid placement/removing unit 121. This provides communication between the atmosphere control unit 122 and the container 101 without the entry of outside air thereinto.

The atmosphere control unit 122 comprises a cavity 107, a gas supply line 109 that is connected to the cavity 107 and is for supplying a gas to the cavity 107, and a gas exhaust line 115. The gas supply line 109 and the gas exhaust line 115 are provided with a gas supply valve 110 and a gas exhaust valve 114, respectively. Thus, the pressure and the gas flow rate in the cavity 107 can be controlled. The gas supply line 109 is provided with a moisture remover 111, a chemical filter 112 and a particle filter 113. Thus, a clean gas can be supplied to the cavity 107.

A lid storage section (not shown) in which the lid 102 removed by the lid placement/removing unit 121 is stored is located at the lower side of the cavity 107, and the lid 102 is transferred to the lid storage section by a lid transport unit 108 so as to be contained in the lid storage section. Furthermore, sensors (not shown) for measuring the concentrations of moisture and chemical substances in the cavity 107 are placed inside the cavity 107.

Four loadports 120 are vertically arranged in the stocker 104 of this embodiment. Therefore, the space occupied in a clean room can be reduced.

A description will be given below of a storage method for semiconductor substrates using the stocker of this embodiment. A high-purity nitrogen (P—N₂) gas having a purity of 99.9999% and a dew point of −90° C. or less is supplied through a gas supply line 109 to a cavity 107 of a stocker 104. Furthermore, the gas supply line 109 is provided with a moisture remover 111, a chemical filter 112 and a particle filter 113, resulting in the further reduced concentrations of moisture and chemical substances and number of ambient foreign particles in the cavity 107. The moisture concentration in the cavity 107 becomes 2% or less, and the number of foreign particles having diameters of 0.12 μm or more is 3 or less per 0.028 m³ (1 cubic foot).

Through the adjustment of a gas supply valve 110 and a gas exhaust valve 114, the pressure in the cavity 107 is set 1.5 through 3 times higher than the atmospheric pressure in a clean room in which the stocker 104 is placed. This can suppress the number of ambient foreign particles without the entry of outside air into the cavity 107. Furthermore, the moisture concentration in the cavity 107 is monitored by a moisture-concentration-measuring sensor. When the monitored moisture concentration is above the normal value in the connection of the cavity 107 with the container 101 or the like, the gas flow rate is increased to raise the pressure in the cavity 107. When the monitored moisture concentration is thereafter stabilized within the normal range, the gas flow rate is restored. Furthermore, a chemical-substance-measuring sensor, such as gas chromatography, is mounted in the cavity 107. Thus, when chemical substances, such as organic materials, inorganic acid and alkaline gases, whose concentration is above the normal value are detected, the gas flow rate can be increased likewise.

A description will be given below of how a container 101 is connected with the stocker 104. First, the container 101 transported by an Over Head Transport (OHT) system is transferred to the top of a delivery table 123. The delivery table 123 extends in synchronization with the OHT system. Therefore, the container 101 is smoothly transferred to the delivery table 123. Subsequently, the delivery table 123 retracts to move the container 101 toward a port door 106. As a result, the container 101 is supported on the supporting table 105.

Subsequently, while the surface of a lid 102 of the container 101 transferred to the supporting table 105 is brought into close contact with the port door 106, the lid 102 is removed from a casing 103 by a lid placement/removing unit 121. The removed lid 102 is stored into the lid storage section in the stocker 104 by the lid transport unit 108. A bar code and a bar-code reader are provided on the lid 102 and the lid placement/removing unit 121, respectively, such that the removed lid 102 can be returned to the associated casing 103.

The container 101 is connected to the stocker 104 by removing the lid 102 from the casing 103. This provides communication between the cavity 107 and the container 101. A P-N₂ gas with which the cavity 107 is filled flows through an open side of the container 101 from which the lid 102 is removed into the container 101. As a result, the inside of the container 101 has the same environment as the cavity 107. Therefore, semiconductor substrates contained in the container 101 can be stored under a clean environment. Furthermore, the cavity 107 is set at a positive pressure while the port door 106 is brought into close contact with the container 101. This prevents outside air from entering into the container 101.

In order to remove the container 101 from the stocker 104, the lid 102 contained in the lid storage section is first returned to the loadport 120 by the lid transport unit 108 and mounted on the casing 103 by the lid placement/removing unit 121, thereby sealing the container 101 and separating the container 101 from the stocker 104. Subsequently, the container 101 is transferred to the OHT system by extending the delivery table 123.

A description will be given below of results obtained by actually storing a semiconductor substrate in the above-mentioned stocker.

FIG. 2 shows the foreign particle deposition percentage at which particles are deposited on a semiconductor substrate contained in the container 101 when the pressures in the cavity 107 and the container 101 are changed. In FIG. 2, the axis of abscissas indicates the pressure (MPa) in the cavity 107, and the axis of ordinates indicates the foreign particle deposition percentage (%).

In the measurement of the foreign particle deposition percentage, the cleanliness of the cavity 107 was stabilized by adjusting the particle filter 113 and the chemical filter 112. Furthermore, a normal RCA-cleaned 12-inch wafer was used as the semiconductor substrate and contained on the lowest stage of the container 101. Furthermore, the container 101 was connected to the lowest loadport of the stocker 104.

The foreign particle deposition percentage was determined as follows: The numbers of 0.12-μm-or-more-diameter foreign particles deposited on the wafer surface before and after the storage of the wafer in the container 101 for three hours were measured using a laser-scattering defect inspection apparatus, and the rate of increase in the number of foreign particles was determined in the following formula (1). Foreign Particle Deposition Percentage=(Number of Foreign Particles After Wafer Storage−Number of Foreign Particles Before Wafer Storage)/Number of Foreign Particles Before Wafer Storage  formula (1)

In this measurement, a differential pressure gage was introduced into a filter incorporated into the container 101, and the pressure in the container 101 was measured by the differential pressure gage. In this case, the respective pressures in the cavity 107 and the container 101 almost coincided with each other.

As shown in FIG. 2, when the pressure in the cavity 107 is increased to some extent, the foreign particle deposition percentage on the wafer decreases. The reason for this is that the increasing pressure in the cavity 107 prevents foreign particles from entering from outside into the cavity 107 and increases the efficiency with which the gas in the container 101 is replaced. However, when the pressure in the cavity 107 is further increased, the foreign particle deposition percentage is conversely increased. The reason for this is considered that the increase in pressure in the cavity 107 produces turbulent air flow in the container 101 and this turbulent air flow picks up foreign particles.

In view of the above, it is appropriate that the pressure in the cavity 107 is 0.15 MPa through 0.3 MPa. This pressure range is 1.5 through 3 times higher than the atmospheric pressure in a clean room in which the stocker 104 is placed.

FIG. 3 shows the relationship between the foreign particle deposition percentage on the surface of each of semiconductor wafers and the number of foreign particles in the cavity 107 when the number of foreign particles is changed. In the measurement of the foreign particle deposition percentage, the pressure in the cavity 107 is 0.2 MPa and a period during which the semiconductor wafers are stored in the container 101 is 3 hours. Ten wafers are put one on every second stage in the container 101. The numbers of 0.12-μm-or-more-diameter foreign particles deposited on each wafer before and after the storage of the wafer were measured by the laser-scattering defect inspection apparatus to determine the average foreign particle deposition percentage among the ten wafers.

As shown in FIG. 3, when the wafer was stored under an environment including three 0.12-μm-or-more-diameter foreign particles or more per one cubic foot, foreign particles were hardly deposited on the wafer. On the other hand, when the wafer was stored under an environment including ten 0.12-μm-or-more-diameter foreign particles per one cubic foot, the number of foreign particles on the wafer surface increased 30% or more. Therefore, the number of foreign particles in the cavity 107 is preferably 3 or less per one cubit foot.

FIG. 4 shows the relationship between the moisture concentration in the cavity 107 and the thickness of a natural oxide film formed on the surface of the semiconductor wafer contained in the container 101. In FIG. 4, the axis of abscissas indicates the moisture concentration (%) and the axis of ordinates indicates the thickness of the natural oxide film (nm).

A 12-inch silicon wafer that was normally RCA-cleaned and then processed for three minutes by hydrofluoric acid with a 1% concentration to remove an oxide film located on its surface was used for the measurement of the moisture concentration and the thickness of the natural oxide film. After the storage of the silicon wafer for five hours, the thickness of the natural oxide film was measured by ellipsometry. Furthermore, the moisture concentration was measured by a wireless moisture measurement device placed in the vicinity of the port door 106.

As shown in FIG. 4, with increase in the moisture concentration, the natural oxide film formed on the wafer surface becomes thicker. In a fabrication process for a semiconductor device, it is desirable that the natural oxide film on the wafer surface has a thickness of one atomic layer or less, i.e., 0.4 nm or less. Therefore, the moisture concentration in the cavity 107 is preferably 2% or less.

According to the stocker of this embodiment, the supplied gas is exhausted from the gas exhaust line 115 in one pass. However, when an expensive gas is used, it is desirable to suppress the usage of the gas. In this case, a gas mixing box 116 and a gas recovery line 124 may be provided as shown in FIG. 5. Thus, a gas exhausted from the gas exhaust valve 114 can be recovered by the gas recovery line 124, and then the recovered gas can be mixed with a gas taken from the gas supply line 109 in the gas mixing box 116. The mixed gases may be circulated through the cavity 107. This circulation system can sharply reduce the usage of gas. Even for this structure, the use of the moisture remover 111, the particle filter 112 and the chemical filter 113 can keep the cleanliness in the cavity 107 within the normal range.

A transport mechanism for taking semiconductor substrates through the open side and an optical-image-comparison defect inspection apparatus are provided in the atmosphere control unit 107. Thus, the surface states of the stored semiconductor substrates can be inspected. This permits the elimination of defective semiconductor substrates from the stored semiconductor substrates and can provide a higher-reliability stocker. Furthermore, since the wait time for the processing of semiconductor substrates can effectively be utilized, the turnaround time (TAT) can be shortened in the fabrication process for semiconductor devices.

Moreover, a plurality of stockers according to this embodiment are combined together as shown in FIG. 6. This can increase the storage capacity, resulting in the more efficiently stored semiconductor substrates.

Although in this embodiment a high-purity nitrogen gas is used as a gas taken into the cavity 107, an inert gas, such as argon or helium, or ultra-dry air may be used instead of nitrogen.

As described above, the stocker of this embodiment can store semiconductor wafers under a clean environment without separately providing any specific mechanism for the container. Although in this embodiment, for example, a front-opening type FOUP is used as the container, this is not restrictive. The use of a bottom-opening type BOUP also provides the same effects.

In the fabrication process for semiconductor devices, semiconductor substrates are stored in the stocker of this embodiment in the process step of storing the semiconductor substrates while waiting for the next process step. This can prevent the semiconductor substrates from being contaminated during the storage of the semiconductor substrates and a natural oxide film from being formed during the storage thereof, thereby providing a high-yielding fabrication process for semiconductor devices. The present invention is useful, in particular, when semiconductor substrates are stored before the gate dielectric formation process step in which a natural oxide film should not be formed. 

1. A stocker for semiconductor substrates, comprising: a container for containing the semiconductor substrates at which semiconductor devices are to be formed, said container being composed of a casing having an open side and a removable lid for sealing the casing at the open side; an atmosphere control unit having a cavity through which a clean gas is passed to keep the inside pressure higher than the outside atmospheric pressure and a gas supply system for supplying the gas to the cavity; and a loadport for connecting the cavity with the container to prevent outside air from entering into the container, wherein the loadport comprises a port door that can be brought into close face-to-face contact with one surface of the lid of the container and a lid placement/removing unit for placing the lid on the container and removing the lid from the container brought into close face-to-face contact with the port door, and the lid placement/removing unit is configured to remove the lid from the container into communication between the cavity and the container, thereby allowing the inside of the container to have the same atmosphere as the cavity.
 2. The stocker of claim 1, wherein a pressure in the cavity is 1.5 through 3 times higher than the outside atmospheric pressure.
 3. The stocker of claim 1, wherein the gas has a moisture concentration of 2% or less and contains three or less 0.12-μm-or-more-diameter foreign particles per one cubic foot.
 4. The stocker of claim 3, wherein the gas is a nitrogen gas, an argon gas, a helium gas, or air.
 5. The stocker of claim 1, wherein the gas supply system has a moisture remover for reducing the moisture concentration in the gas to 2% or less.
 6. The stocker of claim 5, further comprising a gas recovery line for recovering a gas exhausted from the cavity and returning the gas to the gas supply system.
 7. The stocker of claim 1, wherein the gas supply system has at least one of a particle-removing filter for removing particles from the gas by filtering the gas and a chemical filter for removing a chemical substance from the gas by filtering the gas.
 8. The stocker of claim 7, further comprising a gas recovery line for recovering a gas exhausted from the cavity and returning the gas to the gas supply system.
 9. The stocker of claim 1, further comprising: a sensor for measuring the concentration of at least one of moisture, an organic chemical component and an inorganic chemical component in the cavity; and a flow rate control unit for increasing the gas flow rate in the cavity when the measurement result of the sensor is above a predetermined value.
 10. The stocker of claim 1, further comprising: a defect inspection unit for inspecting the surfaces of the semiconductor substrates for defects; and a semiconductor substrate transport system for taking the semiconductor substrates from the container and transferring the semiconductor substrates to the defect inspection unit.
 11. The stocker of claim 1, wherein the loadport further comprises an extendable delivery table for receiving/delivering the container from/to the outside.
 12. The stocker of claim 1, further comprising: a lid storage section for storing a lid removed from the container by the lid placement/removing unit; and a lid transport unit for bidirectionally transferring the removed lid between the lid placement/removing unit and the lid storage section.
 13. The stocker of claim 12, wherein the loadport comprises a plurality of loadports.
 14. The stocker of claim 13 further comprising a recognition unit for, when the lid is removed from the casing, recognizing a combination of the lid and the casing such that the removed lid can again be fitted to the associated casing.
 15. The stocker of claim 1, wherein the container is a front opening unified pod.
 16. A storage method for semiconductor substrates, comprising the steps of: containing semiconductor substrates at which semiconductor devices are to be formed inside a stocker having a cavity through which a clean gas is passed to keep the inside pressure higher than the outside atmospheric pressure, connecting the stocker with a container composed of a casing having an open side and a removable lid for sealing the casing at the open side; opening the lid while preventing outside air from entering into the container, thereby communicating the cavity with the container; and storing the semiconductor substrates while replacing a gas inside the container with a gas with which the cavity is filled.
 17. The method of claim 16, wherein a pressure in the cavity is 1.5 through 3 times higher than the outside atmospheric pressure.
 18. The method of claim 16, wherein the cavity is filled with a gas having a moisture concentration of 2% or less and containing three or less 0.12-μm-or-more-diameter foreign particles per one cubic foot.
 19. The method of claim 18, wherein the gas is a nitrogen gas, an argon gas, a helium gas, or air.
 20. The method of claim 18, wherein a gas exhausted from the cavity is used while being circulated by returning the gas to the cavity.
 21. The method of claim 16, further comprising the step of connecting the cavity to the container through a loadport comprising a port door that can be brought into close face-to-face contact with one surface of the lid of the container and a lid placement/removing unit for placing the lid on the container and removing the lid from the container brought into close face-to-face contact with the port door, said loadport being placed in the cavity.
 22. The method of claim 16, further comprising the steps of: measuring the concentration of at least one of moisture, organic chemical components and inorganic chemical components in the cavity; and increasing the flow rate of a gas supplied to the cavity when the result obtained by measuring the concentration thereof is above a predetermined value.
 23. A fabrication method for a semiconductor device, said method comprising a plurality of process steps for forming a semiconductor device at a semiconductor substrate and a storage step carried out between any two of the plurality of process steps, wherein in the storage step, a stocker to which a container is connected is used, said container containing the semiconductor substrate and being composed of a casing having an open side and a removable lid for sealing the casing at the open side, the stocker comprises: an atmosphere control unit having a cavity through which a gas having a moisture concentration of 2% or less and containing three or less 0.12-μm-or-more-diameter ambient foreign particles per one cubic foot is passed to keep the inside pressure at a positive pressure that is 1.5 through 3 times higher than the outside atmospheric pressure, and a gas supply system for supplying the gas to the cavity; and a loadport for connecting the cavity with the container to prevent outside air from entering into the container, wherein the loadport comprises a port door that can be brought into close face-to-face contact with one surface of the lid of the container and a lid placement/removing unit for placing the lid on the container and removing the lid from the container brought into close face-to-face contact with the port door, and the lid is removed from the container by the lid placement/removing unit so that the cavity is communicated with the container to allow the inside of the container to have the same atmosphere as the cavity. 